Wrap variables in {} for safer interpolation
Change interpolation to concatenation
Replace double quotes with single quotes
minor #3555 Wrap variables in {} for safer interpolation (ifdattic)

This PR was merged into the 2.3 branch.

Discussion
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Wrap variables in {} for safer interpolation

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3
| Fixed tickets |

Commits
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4046476 Replace double quotes with single quotes
0f7a189 Change interpolation to concatenation
d3839ce Wrap variables in {} for safer interpolation